毒扁豆碱对大鼠的镇痛效应及静脉注射毒扁豆碱与蛛网膜下腔注射吗啡的相互作用
作者：陈莲华 Alexander NEMIROVSKY 贡沁燕
单位：陈莲华(上海医科大学 眼耳鼻喉科医院 麻醉科，中国 上海 200031)；Alexander NEMIROVSKY(美国南加州大学 洛杉机医疗中心 麻醉科，美国 洛杉机 90033)；贡沁燕(上海医科大学基础医学院 药理教研室，中国 上海 200032)
关键词：毒扁豆碱；吗啡；疼痛测定；药物协同作用
中国新药与临床杂志000601 [摘要] 目的：观察在术后不同阶段静脉注射胆碱酯酶抑制剂毒扁豆碱对鼠痛阈的影响，以及静注毒扁豆碱和蛛网膜下腔注射吗啡的药物相互作用。方法：6组SD大鼠，置入蛛网膜下腔和股静脉导管。采用辐射热刺激诱发的鼠腿撤退试验测痛阈，测试分别于术后1～3 h和术后3 d进行。动物分别接受静注毒扁豆碱、蛛网膜下腔注射吗啡及两者联合给药。比较术后1～3 h和3 d各种药物对痛阈的影响、联合给药与单独给药对痛阈的影响。药物的镇痛效应以最大可能效应的百分比(%MPE)表示。结果：毒扁豆碱术后1～3 h静注导致%MPE明显提高；毒扁豆碱与吗啡的联合给药效应在术后早期更明显；小剂量联合给药的镇痛作用明显大于双倍剂量单独给药的镇痛作用；联合给药的测得效应值明显大于估计叠加效应值。结论：胆碱酯酶抑制剂毒扁豆碱在术后早期产生镇痛作用；静注毒扁豆碱与蛛网膜下腔注射吗啡的联合给药呈协同效应。
, http://www.100md.com
[中图分类号] R971.91；R965
[文献标识码] A
[文章编号] 1007-7669(2000)06-0433-05
Antinociceptive effect of physostigmine and interaction of intravenous physostigmine with intrathecal morphine in rats
CHEN Lian-Hua
(Department of Anesthesiology, The Eye Ear Nose and Throat Hospital, Shanghai Medical University, SHANGHAI 200031, China)
, 百拇医药
Alexander NEMIROVSKY
(Department of Anesthesiology, Los Angeles Medical Center of the University of South California, CA 90033, USA)
GONG Qin-Yan
(Department of Pharmacology, Shanghai Medical University, SHANGHAI 200032, China)
[ABSTRACT] AIM: To investigate the antinociceptive effect of anticholinesterase agent physostigmine at different postoperative time, and the interaction of intravenous physostigmine with intrathecal morphine in rats. METHODS: Six groups of rats were operated on for intrathecal and intravenous catheterization. Nociceptive responses of hind paws of each animal were measured with “plantar stimulation” test 1-3 h and 3 d postoperatively. Animals received intravenous (iv) physostigmine, intrathecal (ith) morphine, or combination of both. The antinociceptive effect of each group was converted to the percent maximum possible effect (% MPE). RESULTS: Administration of physostigmine 1-3 h after operation resulted in dramatic increase in % MPE. The effects of combinations of iv physostigmine and ith morphine were more pronounced at early postoperative time. The potency of low dose combination was significantly greater than that of double doses of both drugs. The % MPE of the observed effects of all combinations was significantly higher than that of the expected additive effects. CONCLUSION: The antinociception of physostigmine occurs at early postoperative time. The interaction of iv physostigmine with ith morphine indicates their synergistic effect.
, 百拇医药
[KEY WORDS] physostigmine; morphine; pain measurement; drug synergism
[Ucnumber] R 971.91；R 965
[Document code] A
[Article ID] 1007-7669(2000)06-0433-05
Opioids activate opioid receptors and cause analgesia. The effect of opioid receptor activation may ultimately be mediated by some intermediate neurotransmitters. It has been proved that one of the important inhibitory neurotransmitters in response to noxious stimulation is norepinephrine (NE). In sheep and humans, cerebrospinal fluid (CSF) NE and acetylcholine (Ach) concentrations increased after acute painful stimulation[1] and intravenous opioid administration[2]. In human volunteers, intrathecal cholinesterase inhibitor neostigmine caused the increase in CSF Ach concentration, resulted in analgesia and enhanced the effect of opioids injected systemically. It has been hypothesized that either pain stimulation or opioid administration may induce the release of NE which in turn activates the cholinergic neuron in spinal dorsal horn to release Ach and cause analgesia[4]. Therefore, the current study was designed to investigate the antinociceptive effect of anticholinesterase agent physostigmine at different postoperative time in rats, and to evaluate the interaction of intravenous (iv) physostigmine with intrathecal (ith) morphine.
, 百拇医药
MATERIALS AND METHODS
Animal preparation Male, 300-350 g Sprague-Dawley rats were used. Animals were housed individually in a temperature controlled room with a 12 h light-dark cycle, and fed with both food and water available ad libitum. Experiments were performed during the light cycle. Under halothane anesthesia, a chronic catheterization of the lumbar subarachnoid space was performed for the ith injection. Briefly, a PE 10 catheter was inserted through the atlanto-occipital membrane and introduced to a length of 10 cm caudalward into the lumbar subarachnoid space. The catheter was then fixed to the back neck of the animal. A concurrent catheterization of the femoral vein was performed for intravenous injection. The animals which exhibited no signs of neurological deficit after recovery from the anesthesia underwent the experiment procedure.
, 百拇医药
Nociceptive threshold test Nociceptive responses of hind paws of each animal were measured by means of “plantar stimulation” test using a device designed and made by Yaksh's laboratory[5] (University of California, San Diego, USA). The rats were placed in a clear plastic cage on an elevated floor of clear glass. To reduce the variability, the under-floor temperature was maintained at 30℃. A radiant heat source from a 50 W, 8 V lamp was contained in a movable holder placed beneath the glass floor. The radiant heat diameter was 4 mm and bulb intensity was controlled at 5.25 A. To initiate a test, the under-floor heat source was positioned to focus at the plantar surface of one hind paw which was completely in contact with the glass. The light was then started meanwhile the timing circuit was initiated automatically. The nociceptive response was determined by the interval from the application of the light beam to the hind paw withdrawal. A cutoff time which was three times of the baseline nociceptive response latency was set in order to avoid tissue burn injury.
, 百拇医药
Test Protocol Each rat was used in one dosage regime only. Initially, baseline nociceptive response latency was determined by the average of three measurements. Subsequently, drug administration was performed in a blind fashion. After drug injection, nociceptive response latency of the hind paw was measured at 5 min intervals until the baseline response was regained. The peak time of antinociceptive effect and the duration of the effect were determined. Different groups of rats were scheduled to receive iv physostigmine 50 or 100 μg*kg-1, ith morphine 1 or 2 μg, or the combinations of iv physostigmine (50 or 100 μg*kg-1) with concurrent ith morphine 1 μg, respectively. All drugs were dissolved in Ringer's solution and administered in an injection volume of 1 mL*kg-1 for iv and 10 μL for ith. Following each ith injection, the catheter was flushed with 10 μL Ringer's solution to ensure the drug delivery into ith space. The tests were performed at 1-3 h after the ith and iv catheterization when the rats completely recovered from anesthesia. To compare the antinociceptive effect of each drug in the animals with or without postoperative stress, the tests for the same drug doses were repeated three days later in the same rats.
, 百拇医药
At the end of the experiments, all rats received an ith injection of 10 μL of 2% lidocaine. Data from rats who did not develop motor paralysis within 2 min were excluded.
Statistical analysis The response latency was converted to the percent maximum possible effect (% MPE) which was calculated by the following formula:
Where postdrug response latency=the longest response latency observed after drug administration, baseline response latency=the average of three measures of the response latency before drug administration, and cutoff time=15 s.
, 百拇医药
Comparisons of the drug effects between different postoperative time were performed. The observed effects of the combinations were compared with the expected additive effects calculated from the individual drugs. All data were expressed as mean±standard deviation. Statistical analysis was carried out with student-t-test. A P value<0.05 was considered significant.
RESULTS
The nociceptive response latency of the six rats was tested preoperatively, 1-3 h and 3 d postoperatively. The results showed no significant differences, which meant the baseline nociceptive response was not noticeably affected by the operation.
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Morphine ith significantly increased the %MPE, and no difference was found between the effects during two postoperative periods. Physostigmine iv 50 or 100 μg*kg-1 injected 3 d after the operation did not show obvious changes of the %MPE. But physostigmine iv 50 or 100 μg*kg-1 administered 1-3 h after the operation dramatically increased the %MPE. Combined administration of iv physostigmine and ith morphine resulted in marked increase in %MPE which was more potent in higher physostigmine dosage. The effects of the combinations were more pronounced at early postoperative time. Table 1 shows the %MPE of each drug administered at different postoperative time.
, 百拇医药
Table 1 % MPE of each drug and combination administered at 1-3 h and 3 d postoperatively drug dosage
rats
1-3 h
3 d
Mor 1 μg
8
12±7a
17±7
Mor 2 μg
7
, 百拇医药
29±8a
20±12
Phys 50 μg*kg-1
8
19±7a
12±2
Phys 100 μg*kg-1
6
35±10c
14±12
Phys 50+Mor.1
, http://www.100md.com
7
62±14c
33±8
Phys 100+Mor.1
8
90±9b
68±16
a P>0.05, bP<0.05, cP<0.01 vs the same dose injected 3 d postoperatively.
Mor means ith morphine; Phys means iv physostigmine; Phys 50+Mor 1 means iv physostigmine 50 μg*kg-1+ith morphine 1 μg; Phys 100+Mor 1 means iv physostigmine 100 μg*kg-1+ith morphine 1 μg.
, 百拇医药
According to Berenbaum's[6] definition, non-additive interaction of drugs is present when the effect of a combination of drugs differs from that expected from their individual dose response curves. If both drugs act in an additive manner, then one of the drugs can be replaced by the second in amount equieffective to the amount of the first drug. Therefore, the expected effect of the combination lies between the effects of double doses of both drugs and never exceeds both of them. If at any dose level response to the combination of drugs is significantly greater than the response to the double doses of both drugs, then the interaction of the drugs is synergistic. Thus, in this study, the observed effect of the combination of small doses of morphine and physostigmine has been compared to the effect of double doses of both drugs. Figure 1 shows the time-response of the ith morphine 2 μg, iv physostigmine 100 μg*kg-1, and ith morphine 1 μg+iv physostigmine 50 μg*kg-1. The effect of the low dose combination was obviously greater than that of the double doses of both drugs. Figure 2
, 百拇医药
Fig 1 Time-response of the effect of intrathecal morphine 2 μg, intravenous physostigmine 100 μg*kg-1, and morphine 1 μg+physostigmine 50 μg*kg-1 on paw withdrawal latencies.
All points represent the mean response latencies of 6-8 animals, and error bars denote SD.
Fig 2 Comparison of the observed combined effect and the expected additive effect
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The observed effect of each combination was significantly greater than the expected additive effect (P<0.01). All bars represent the mean % MPE of 6-8 animals, and error bars denote SD.shows the comparison of the observed mixed effects of the two doses of combinations with the expected additive effects calculated from the effect of morphine and physostigmine injected separately. The potency of the observed effects of the combinations was significantly greater than that of the expected additive effects.
, 百拇医药
DISCUSSION
Observations indicate that a descending inhibitory pathway exists from the mid-brain and medulla to the spinal cord dorsal horn in modulating analgesia. Chief neurotransmitters involved are NE and Ach. Plenty of evidence has been found. Ith administration of the antagonist of acetylcholine muscarinic receptor atropine powerfully reduced the analgesia induced by systemic morphine, but this effect failed to appear in spinal cord transected rats[7]. In sheep and humans, iv injection of morphine caused increase in concentration of NE and Ach in the CSF from lumbar spinal space[2]. The exact relationship between NE and Ach in analgesic mechanism is not clear yet. It has been hypothesized that any noxious stimulation or opioid administration may activate the pathway from supraspinal central sites to spinal cord and cause the release of NE. Then the released NE may mediate cholinergic neurons to produce Ach, which diminishes substance P released from primary afferent neurons and reduces response of dorsal horn neurons to noxious stimulation[1，4]. This hypothesis becomes the theoretical background for the application of anticholinesterase agents in pain management. In the current study, it is proved that physostigmine enhanced the antinociception of morphine, which is coincidentwith the previous reports[3]. But the antinociception of physostigmine alone appeared only at early postoperative time. Furthermore, the combined effect of iv physostigmine and ith morphine was more pronounced at early postoperative period. Since the antinociceptive effect of morphine ith showed no significant changes during the two postoperative periods, the differences of the antinociception of physostigmine and the combination should not be explained by the tolerance of the drugs. The reason for this phenomenon is probably due to the activation of endogenous Ach by the postoperative stress stimulation. Physostigmine, which can pass the blood-brain barrier, may produce more effect on enhancement of the decending inhibitory analgesic modulation by further increasing the Ach concentration.
, 百拇医药
Both opioids and anticholinesterase agents have some dose-dependent side effects. The most dangerous side effect of opioids is respiratory depression. Physostigmine can cause sedation, nausea, leg weakness and even muscle tremble. If the combination of the two drugs produces a synergistic effect, the desirable dosage of both drugs can be decreased, thus the incidence of undesirable effects can be reduced. According to pharmacological theory, if the combined effect of the two drugs is obviously greater than the expected additive effect of them at any dose level, then the interaction of the drugs is synergism[6]. Therefore, the results of the present study suggest that there is a synergistic interaction between iv physostigmine and ith morphine. In addition, it is reported that anticholinesterase agents can antagonize the respiratory depression induced by morphine[8]. It can be expected that this combination may lead to some advancement in pain management.
, 百拇医药
Conclusions: anticholinesterase agent physostigmine produces antinociception under the condition that exists postoperative stress there. The combination of iv physostigmine and ith morphine results in synergistic interaction.
[Biography] CHEN Lian-Hua(1964-)，female，the Zhejiang province people, associated professor, master, be engaged in clinical anaesthesia and scientific research.
[Correspondence author] CHEN Lian-Hua. Phn: 86-21-64377134,ext 511
, 百拇医药
[REFERENCES]
[1] Eisenach JC, Detweiler DJ, Tong C, Angelo RD, Hood DD. Cerebrospinal fluid norepinephrine and acetylcholine concentrations during acute pain [J]. Anesth Analg, 1996, 82:621-626.
[2] Bouaziz H, Tong C, Yoon Y, Hood DD, Eisenach JC. Intravenous opioids stimulate norepinephrine and acetylcholine release in spinal cord dorsal horn [J]. Anesthesiology, 1996, 84:143-154.
[3] Hood DD, Mallak KA, James RL, Tuttle R, Eisenach JC. Enhancement of analgesia from systemic opioid in humans by spinal cholinesterase inhibition [J]. J pharmacol Exp Ther, 1997,282:86-92.
, 百拇医药
[4] Detweiler DJ, Eisenach JC, Tong C, Jackson C. A cholinergic interaction in alpha2 adrenocepter-mediated antinociception in sheep [J]. J pharmacol Exp Ther, 1993, 265:536-542.
[5] Naguib M, Yaksh TL. Antinociceptive effects of spinal cholinesterase inhibition and isobolographic analysis of the interaction with μ and α2 receptor systems [J]. Anesthesiology, 1994, 80:1338-1348.
[6] Berenbaum MC. What is synergy?[J]. Pharmacol Rev, 1989,41:93-141.
, 百拇医药
[7] Chiang CY, Zhuo M. Evidence for the involvement of a descending cholinergic pathway in systemic morphine analgesia [J]. Brain Res, 1989,478:293-300.
[8] Elmalem E, Chorev M, Weinstock M. Antagonism of morphine-induced respiratory depression by novel anticholinesterase agents [J]. Neuropharmacology, 1991,30:1059-1064.
[Received date] 2000-01-07
[Accepted date] 2000-07-25, http://www.100md.com
单位：陈莲华(上海医科大学 眼耳鼻喉科医院 麻醉科，中国 上海 200031)；Alexander NEMIROVSKY(美国南加州大学 洛杉机医疗中心 麻醉科，美国 洛杉机 90033)；贡沁燕(上海医科大学基础医学院 药理教研室，中国 上海 200032)
关键词：毒扁豆碱；吗啡；疼痛测定；药物协同作用
中国新药与临床杂志000601 [摘要] 目的：观察在术后不同阶段静脉注射胆碱酯酶抑制剂毒扁豆碱对鼠痛阈的影响，以及静注毒扁豆碱和蛛网膜下腔注射吗啡的药物相互作用。方法：6组SD大鼠，置入蛛网膜下腔和股静脉导管。采用辐射热刺激诱发的鼠腿撤退试验测痛阈，测试分别于术后1～3 h和术后3 d进行。动物分别接受静注毒扁豆碱、蛛网膜下腔注射吗啡及两者联合给药。比较术后1～3 h和3 d各种药物对痛阈的影响、联合给药与单独给药对痛阈的影响。药物的镇痛效应以最大可能效应的百分比(%MPE)表示。结果：毒扁豆碱术后1～3 h静注导致%MPE明显提高；毒扁豆碱与吗啡的联合给药效应在术后早期更明显；小剂量联合给药的镇痛作用明显大于双倍剂量单独给药的镇痛作用；联合给药的测得效应值明显大于估计叠加效应值。结论：胆碱酯酶抑制剂毒扁豆碱在术后早期产生镇痛作用；静注毒扁豆碱与蛛网膜下腔注射吗啡的联合给药呈协同效应。
, http://www.100md.com
[中图分类号] R971.91；R965
[文献标识码] A
[文章编号] 1007-7669(2000)06-0433-05
Antinociceptive effect of physostigmine and interaction of intravenous physostigmine with intrathecal morphine in rats
CHEN Lian-Hua
(Department of Anesthesiology, The Eye Ear Nose and Throat Hospital, Shanghai Medical University, SHANGHAI 200031, China)
, 百拇医药
Alexander NEMIROVSKY
(Department of Anesthesiology, Los Angeles Medical Center of the University of South California, CA 90033, USA)
GONG Qin-Yan
(Department of Pharmacology, Shanghai Medical University, SHANGHAI 200032, China)
[ABSTRACT] AIM: To investigate the antinociceptive effect of anticholinesterase agent physostigmine at different postoperative time, and the interaction of intravenous physostigmine with intrathecal morphine in rats. METHODS: Six groups of rats were operated on for intrathecal and intravenous catheterization. Nociceptive responses of hind paws of each animal were measured with “plantar stimulation” test 1-3 h and 3 d postoperatively. Animals received intravenous (iv) physostigmine, intrathecal (ith) morphine, or combination of both. The antinociceptive effect of each group was converted to the percent maximum possible effect (% MPE). RESULTS: Administration of physostigmine 1-3 h after operation resulted in dramatic increase in % MPE. The effects of combinations of iv physostigmine and ith morphine were more pronounced at early postoperative time. The potency of low dose combination was significantly greater than that of double doses of both drugs. The % MPE of the observed effects of all combinations was significantly higher than that of the expected additive effects. CONCLUSION: The antinociception of physostigmine occurs at early postoperative time. The interaction of iv physostigmine with ith morphine indicates their synergistic effect.
, 百拇医药
[KEY WORDS] physostigmine; morphine; pain measurement; drug synergism
[Ucnumber] R 971.91；R 965
[Document code] A
[Article ID] 1007-7669(2000)06-0433-05
Opioids activate opioid receptors and cause analgesia. The effect of opioid receptor activation may ultimately be mediated by some intermediate neurotransmitters. It has been proved that one of the important inhibitory neurotransmitters in response to noxious stimulation is norepinephrine (NE). In sheep and humans, cerebrospinal fluid (CSF) NE and acetylcholine (Ach) concentrations increased after acute painful stimulation[1] and intravenous opioid administration[2]. In human volunteers, intrathecal cholinesterase inhibitor neostigmine caused the increase in CSF Ach concentration, resulted in analgesia and enhanced the effect of opioids injected systemically. It has been hypothesized that either pain stimulation or opioid administration may induce the release of NE which in turn activates the cholinergic neuron in spinal dorsal horn to release Ach and cause analgesia[4]. Therefore, the current study was designed to investigate the antinociceptive effect of anticholinesterase agent physostigmine at different postoperative time in rats, and to evaluate the interaction of intravenous (iv) physostigmine with intrathecal (ith) morphine.
, 百拇医药
MATERIALS AND METHODS
Animal preparation Male, 300-350 g Sprague-Dawley rats were used. Animals were housed individually in a temperature controlled room with a 12 h light-dark cycle, and fed with both food and water available ad libitum. Experiments were performed during the light cycle. Under halothane anesthesia, a chronic catheterization of the lumbar subarachnoid space was performed for the ith injection. Briefly, a PE 10 catheter was inserted through the atlanto-occipital membrane and introduced to a length of 10 cm caudalward into the lumbar subarachnoid space. The catheter was then fixed to the back neck of the animal. A concurrent catheterization of the femoral vein was performed for intravenous injection. The animals which exhibited no signs of neurological deficit after recovery from the anesthesia underwent the experiment procedure.
, 百拇医药
Nociceptive threshold test Nociceptive responses of hind paws of each animal were measured by means of “plantar stimulation” test using a device designed and made by Yaksh's laboratory[5] (University of California, San Diego, USA). The rats were placed in a clear plastic cage on an elevated floor of clear glass. To reduce the variability, the under-floor temperature was maintained at 30℃. A radiant heat source from a 50 W, 8 V lamp was contained in a movable holder placed beneath the glass floor. The radiant heat diameter was 4 mm and bulb intensity was controlled at 5.25 A. To initiate a test, the under-floor heat source was positioned to focus at the plantar surface of one hind paw which was completely in contact with the glass. The light was then started meanwhile the timing circuit was initiated automatically. The nociceptive response was determined by the interval from the application of the light beam to the hind paw withdrawal. A cutoff time which was three times of the baseline nociceptive response latency was set in order to avoid tissue burn injury.
, 百拇医药
Test Protocol Each rat was used in one dosage regime only. Initially, baseline nociceptive response latency was determined by the average of three measurements. Subsequently, drug administration was performed in a blind fashion. After drug injection, nociceptive response latency of the hind paw was measured at 5 min intervals until the baseline response was regained. The peak time of antinociceptive effect and the duration of the effect were determined. Different groups of rats were scheduled to receive iv physostigmine 50 or 100 μg*kg-1, ith morphine 1 or 2 μg, or the combinations of iv physostigmine (50 or 100 μg*kg-1) with concurrent ith morphine 1 μg, respectively. All drugs were dissolved in Ringer's solution and administered in an injection volume of 1 mL*kg-1 for iv and 10 μL for ith. Following each ith injection, the catheter was flushed with 10 μL Ringer's solution to ensure the drug delivery into ith space. The tests were performed at 1-3 h after the ith and iv catheterization when the rats completely recovered from anesthesia. To compare the antinociceptive effect of each drug in the animals with or without postoperative stress, the tests for the same drug doses were repeated three days later in the same rats.
, 百拇医药
At the end of the experiments, all rats received an ith injection of 10 μL of 2% lidocaine. Data from rats who did not develop motor paralysis within 2 min were excluded.
Statistical analysis The response latency was converted to the percent maximum possible effect (% MPE) which was calculated by the following formula:
Where postdrug response latency=the longest response latency observed after drug administration, baseline response latency=the average of three measures of the response latency before drug administration, and cutoff time=15 s.
, 百拇医药
Comparisons of the drug effects between different postoperative time were performed. The observed effects of the combinations were compared with the expected additive effects calculated from the individual drugs. All data were expressed as mean±standard deviation. Statistical analysis was carried out with student-t-test. A P value<0.05 was considered significant.
RESULTS
The nociceptive response latency of the six rats was tested preoperatively, 1-3 h and 3 d postoperatively. The results showed no significant differences, which meant the baseline nociceptive response was not noticeably affected by the operation.
, http://www.100md.com
Morphine ith significantly increased the %MPE, and no difference was found between the effects during two postoperative periods. Physostigmine iv 50 or 100 μg*kg-1 injected 3 d after the operation did not show obvious changes of the %MPE. But physostigmine iv 50 or 100 μg*kg-1 administered 1-3 h after the operation dramatically increased the %MPE. Combined administration of iv physostigmine and ith morphine resulted in marked increase in %MPE which was more potent in higher physostigmine dosage. The effects of the combinations were more pronounced at early postoperative time. Table 1 shows the %MPE of each drug administered at different postoperative time.
, 百拇医药
Table 1 % MPE of each drug and combination administered at 1-3 h and 3 d postoperatively drug dosage
rats
1-3 h
3 d
Mor 1 μg
8
12±7a
17±7
Mor 2 μg
7
, 百拇医药
29±8a
20±12
Phys 50 μg*kg-1
8
19±7a
12±2
Phys 100 μg*kg-1
6
35±10c
14±12
Phys 50+Mor.1
, http://www.100md.com
7
62±14c
33±8
Phys 100+Mor.1
8
90±9b
68±16
a P>0.05, bP<0.05, cP<0.01 vs the same dose injected 3 d postoperatively.
Mor means ith morphine; Phys means iv physostigmine; Phys 50+Mor 1 means iv physostigmine 50 μg*kg-1+ith morphine 1 μg; Phys 100+Mor 1 means iv physostigmine 100 μg*kg-1+ith morphine 1 μg.
, 百拇医药
According to Berenbaum's[6] definition, non-additive interaction of drugs is present when the effect of a combination of drugs differs from that expected from their individual dose response curves. If both drugs act in an additive manner, then one of the drugs can be replaced by the second in amount equieffective to the amount of the first drug. Therefore, the expected effect of the combination lies between the effects of double doses of both drugs and never exceeds both of them. If at any dose level response to the combination of drugs is significantly greater than the response to the double doses of both drugs, then the interaction of the drugs is synergistic. Thus, in this study, the observed effect of the combination of small doses of morphine and physostigmine has been compared to the effect of double doses of both drugs. Figure 1 shows the time-response of the ith morphine 2 μg, iv physostigmine 100 μg*kg-1, and ith morphine 1 μg+iv physostigmine 50 μg*kg-1. The effect of the low dose combination was obviously greater than that of the double doses of both drugs. Figure 2
, 百拇医药
Fig 1 Time-response of the effect of intrathecal morphine 2 μg, intravenous physostigmine 100 μg*kg-1, and morphine 1 μg+physostigmine 50 μg*kg-1 on paw withdrawal latencies.
All points represent the mean response latencies of 6-8 animals, and error bars denote SD.
Fig 2 Comparison of the observed combined effect and the expected additive effect
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The observed effect of each combination was significantly greater than the expected additive effect (P<0.01). All bars represent the mean % MPE of 6-8 animals, and error bars denote SD.shows the comparison of the observed mixed effects of the two doses of combinations with the expected additive effects calculated from the effect of morphine and physostigmine injected separately. The potency of the observed effects of the combinations was significantly greater than that of the expected additive effects.
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DISCUSSION
Observations indicate that a descending inhibitory pathway exists from the mid-brain and medulla to the spinal cord dorsal horn in modulating analgesia. Chief neurotransmitters involved are NE and Ach. Plenty of evidence has been found. Ith administration of the antagonist of acetylcholine muscarinic receptor atropine powerfully reduced the analgesia induced by systemic morphine, but this effect failed to appear in spinal cord transected rats[7]. In sheep and humans, iv injection of morphine caused increase in concentration of NE and Ach in the CSF from lumbar spinal space[2]. The exact relationship between NE and Ach in analgesic mechanism is not clear yet. It has been hypothesized that any noxious stimulation or opioid administration may activate the pathway from supraspinal central sites to spinal cord and cause the release of NE. Then the released NE may mediate cholinergic neurons to produce Ach, which diminishes substance P released from primary afferent neurons and reduces response of dorsal horn neurons to noxious stimulation[1，4]. This hypothesis becomes the theoretical background for the application of anticholinesterase agents in pain management. In the current study, it is proved that physostigmine enhanced the antinociception of morphine, which is coincidentwith the previous reports[3]. But the antinociception of physostigmine alone appeared only at early postoperative time. Furthermore, the combined effect of iv physostigmine and ith morphine was more pronounced at early postoperative period. Since the antinociceptive effect of morphine ith showed no significant changes during the two postoperative periods, the differences of the antinociception of physostigmine and the combination should not be explained by the tolerance of the drugs. The reason for this phenomenon is probably due to the activation of endogenous Ach by the postoperative stress stimulation. Physostigmine, which can pass the blood-brain barrier, may produce more effect on enhancement of the decending inhibitory analgesic modulation by further increasing the Ach concentration.
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Both opioids and anticholinesterase agents have some dose-dependent side effects. The most dangerous side effect of opioids is respiratory depression. Physostigmine can cause sedation, nausea, leg weakness and even muscle tremble. If the combination of the two drugs produces a synergistic effect, the desirable dosage of both drugs can be decreased, thus the incidence of undesirable effects can be reduced. According to pharmacological theory, if the combined effect of the two drugs is obviously greater than the expected additive effect of them at any dose level, then the interaction of the drugs is synergism[6]. Therefore, the results of the present study suggest that there is a synergistic interaction between iv physostigmine and ith morphine. In addition, it is reported that anticholinesterase agents can antagonize the respiratory depression induced by morphine[8]. It can be expected that this combination may lead to some advancement in pain management.
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Conclusions: anticholinesterase agent physostigmine produces antinociception under the condition that exists postoperative stress there. The combination of iv physostigmine and ith morphine results in synergistic interaction.
[Biography] CHEN Lian-Hua(1964-)，female，the Zhejiang province people, associated professor, master, be engaged in clinical anaesthesia and scientific research.
[Correspondence author] CHEN Lian-Hua. Phn: 86-21-64377134,ext 511
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[Received date] 2000-01-07
[Accepted date] 2000-07-25, http://www.100md.com